题解(easy~)

#include <iostream>
#include <vector>
#include <unordered_map>
using namespace std;
 
int main() {
    int n;
    cin >> n;
    vector<vector<int>> matrix(n + 1, vector<int>(n + 1));
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= n; ++j) {
            cin >> matrix[i][j];
        }
    }
    vector<vector<int>> row_prefix(n + 1, vector<int>(n + 1));
    for (int i = 1; i <= n; ++i) {
        row_prefix[i][0] = 0;
        for (int j = 1; j <= n; ++j) {
            row_prefix[i][j] = row_prefix[i][j - 1] + matrix[i][j];
        }
    }
 
    int ans = 0;
    for (int c1 = 1; c1 <= n; ++c1) {
        for (int c2 = c1; c2 <= n; ++c2) {
            int L = c2 - c1 + 1;
            vector<int> sum_row(n + 1, 0);
            for (int i = 1; i <= n; ++i) {
                sum_row[i] = row_prefix[i][c2] - row_prefix[i][c1 - 1];
            }
            vector<int> pre_sum(n + 1, 0);
            for (int k = 1; k <= n; ++k) {
                pre_sum[k] = pre_sum[k - 1] + sum_row[k];
            }
            unordered_map<int, int> hash_map;
            hash_map[0]  = 1; 
            int current_ans = 0;
            for (int k = 1; k <= n; ++k) {
                int current_val = 2 * pre_sum[k] - L * k;
                current_ans += hash_map[current_val];
                hash_map[current_val]++;
            }
            ans += current_ans;
        }
    }
 
    cout << ans << endl;
    return 0;
}